Brain holds the key to lost memories

People may permanently store memories in their brains, even if they cannot consciously recall them, according to a study by researchers at Duke University in Durham, NC.

"This finding provides insight into a fundamental neurological process and may also help us develop a tool for identifying so-called lost memories," said Roberto Cabeza, Ph.D., an associate professor of psychology and neuroscience in the Duke Center for Cognitive Neuroscience.

One possible future practical application of such a memory tool may be as a lie detector, the researchers suggest. The team's findings were published in the May 24 edition of the Journal of Neuroscience.

Cabeza and colleagues used functional MRI to detect brain activity in the medial temporal lobes of test subjects exposed to "new" and "old" experiences. The medial temporal lobes are known to play a role in a person's ability to remember whether or not an event occurred in the past.

The researchers first showed 16 study subjects a list of words. The subjects were then placed in an MR scanner and shown another list of words. Some of these were old words that were previously viewed and others new words not previously viewed.

When subjects viewed an old word, they exhibited heightened activity in the rear portion of the medial temporal lobes, whether or not they correctly stated that the word was old, Cabeza said.

"This indicates that the brain has the correct answer even if we don't consciously think we've seen the word before," he said.

So why would a person make a mistake when asked about an event, if his or her brain holds the correct answer?

The researchers found that when a subject correctly reported seeing a new word, the scanner demonstrated heightened activity mainly in a front portion of the lobes, rather than in the rear portion. But when a subject mistakenly classified as new a word that was actually old, activity increased in both parts of the medial temporal lobes.

This may lead the medial temporal lobes to give mixed messages, resulting in an incorrect conscious response, Cabeza said.

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